Wakefulness and sleep

Question 1

Endogenous circannual rhythm:

Answer 1

An internal calendar that prepares a species for annual seasonal changes.

Question 2

Endogenous circadian rhythm:

Answer 2

Internal rhythms that last about a day (e.g., wakefulness and sleepiness).

Question 3

Zeitgeber:

Answer 3

Stimulus that is necessary for resetting the circadian rhythm. Light is the dominant zeitgeber for land animals.
Examples:
2. Astronauts exposed to 45 minute intervals of light and dark are never fully alert during their wakeful periods and they sleep poorly during their rest periods.
3. Most people are ill-rested and inefficient for days after the shift to daylight savings time.
4. Blind people sometimes use other zeitbegers (noise, temperature, meals, etc.) but those not sensitive enough to secondary zeitbegers often experience insomnia at night and sleepiness during the day.

Question 4

Jet lag:

Answer 4

A disruption of our biological rhythms due to crossing time zones.

b. Phase-delay: What happens to our circadian rhythms when we travel west, as we stay awake late and awaken the next day already partly adjusted to the new schedule.
c. Phase-advance: What happens to our circadian rhythms when we travel east, as we tend to sleep and awaken earlier than usual.
d. Recent studies have indicated that repeated adjustments of the circadian rhythm can increase levels of cortisol, which can damage the hippocampus and cause memory loss.

Question 5

The Suprachiasmatic Nucleus (SCN)

Answer 5

a. Nucleus located above the optic chiasm in the hypothalamus. The SCN controls the rhythms for sleep and temperature. The neurons of the SCN generate impulses that follow a circadian rhythm.
b. If the SCN is damaged, the body’s rhythms become erratic

Question 6

retinohypothalamic path and SCN:

Answer 6

a. The SCN is reset by the retinohypothalamic path that extends directly from the retinal ganglian cells (in the retina) to the SCN.
b. The retinal ganglion cells that reset the SCN are different from the ganglion cells that contribute to vision and have their own photopigment called melanopsin that responds to slow changes in overall duration of light.
c. These special ganglion cells are located near the nose, not evenly throughout the retina. This way, blind people have enough input to the melanopsin- containing ganglion cells to entrain their waking and sleeping cycle to the local pattern of sunlight.

Question 7

Melatonin:

Answer 7

a. SCN regulates waking and sleeping by controlling the pineal gland which releases the hormone melatonin, which increases sleepiness. Melatonin release usually starts 2 or 3 hours before bedtime.
b. Melatonin stimulates receptors in the SCN to reset the biological clock.

Question 8

Coma:

Answer 8

An extended period of unconsciousness caused by head trauma, stroke, or disease. Characterized by low brain activity throughout the day and little or no response to stimuli, including pain.

Question 9

Vegetative State:

Answer 9

A person alternates between periods of sleep and moderate arousal, although they show no awareness of their surroundings.

Question 10

Minimally Conscious State:

Answer 10

A person shows occasional, brief periods of purposeful actions and limited speech comprehension.

Question 11

Brain Death:

Answer 11

No sign of brain activity and no response to stimulation. In this case, physicians generally wait 24 hours before pronouncing death.

Question 12

Polysomnograph:

Answer 12

A combination of EEG and eye-movement records.

Question 13

Alpha waves:

Answer 13

have a frequency of about 8-12 brain waves per second; these waves are typical of a relaxed state of consciousness.

Question 14

Stages of sleep:

Answer 14

• Stage 1 sleep is a stage of light sleep noted by the presence of irregular, jagged, low-voltage waves.
• Stage 2 sleep is characterized by sleep spindles (a burst of 12-14 Hz waves that last approximately 0.5 second) and K-complexes (sharp, high-amplitude waves followed by a smaller, positive wave).
• Stages 3 and 4 are known as slow-wave sleep (SWS), which is comprised of slow, large-amplitude waves.

Question 15

Paradoxical sleep (or REM):

Answer 15

Sleep stage discovered in cats in which the brain is very active but muscles are completely relaxed. Named “paradoxical” because it is deep sleep in some ways and light in others.

Question 16

Rapid eye movement (REM) sleep:

Answer 16

Same as paradoxical sleep. Researchers discovered that repeated eye movements were associated with paradoxical sleep. Also characterized by fast low-voltage brain waves, plus breathing and heart rates similar to stage 1 sleep. Paradoxical sleep is synonymous with REM sleep, except that many animal species lack eye movements.

Question 17

Non-REM (NREM) sleep:

Answer 17

The stages of sleep other than REM.

Question 18

Sequential stages of sleep:

Answer 18

• When people fall asleep, they enter stage 1, followed by stages 2, 3, and 4, in that order. Then they cycle back from stage 4 through stages 3, 2, and then enter rapid eye movement (REM) sleep.
• After entering REM sleep, the sleep cycle sequence repeats, with each complete cycle lasting 90 minutes.
• Early in the night, stages 3 and 4 predominate, but toward morning, stage 4 grows shorter and REM grows longer.
• REM sleep is associated with dreaming, but dreams can happen in non-REM sleep.

Question 19

Reticular formation:

Answer 19

A structure that extends from the medulla into the forebrain. Lesions through the reticular formation decrease arousal.

Question 20

Pontomesencephalon:

Answer 20

A part of the reticular formation that contributes to cortical arousal. Stimulation of the pontomesencephalon awakens a sleeping individual or increases alertness in someone already awake.

Question 21

Locus coeruleus:

Answer 21

A structure in the pons that is inactive at most times but emits impulses, releasing norepinephrine, in response to meaningful events. The locus coeruleus is also important for storing information. The locus coeruleus is usually silent during sleep.

Question 22

orexin (also called hypocretin):

Answer 22

Orexin is necessary for staying awake.

Question 23

Sleep depends on:

Answer 23

• GABA-mediated inhibition. While spontaneously active neurons continue to fire at a normal rate, we are unconscious because GABA inhibits synaptic activity.

Question 24

Brain Function in REM Sleep:

Answer 24

• During REM sleep, activity increases in the pons, the limbic system, and the parietal and temporal cortex of the brain.
• Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex.

Question 25

PGO (pons-geniculate-occipital) waves:

Answer 25

A distinctive pattern of high-amplitude electrical potentials associated with REM sleep. The waves are detected first in the pons, shortly afterward in the lateral geniculate nucleus of the thalamus, and then in the occipital cortex.

Question 26

REM sleep depends on:

Answer 26

both serotonin and acetylcholine activity for its onset and continuation. Stimulation of acetylcholine synapses quickly moves a sleeper into REM, and serotonin interrupts or shortens REM sleep.

Question 27

Insomnia:

Answer 27

Inadequate sleep characterized by how one feels the following day.

2. Insomnia can result from a number of causes, including noise, uncomfortable temperatures, stress, pain, diet, and medications. Certain psychiatric and neurological disorders (e.g., epilepsy, Parkinson’s disease, brain tumors, depression, and anxiety) are also associated with insomnia.
3. Insomnia may be due to shifts in circadian rhythms (e.g., trying to sleep while body temperature rises).
   a. Phase delayed: shift in rhythm where someone has trouble falling asleep at the usual time.
   b. Phase advanced: shift in rhythm where someone falls asleep easily but awakens early.

Question 28

Narcolepsy

Answer 28

a. A disorder characterized by frequent unexpected periods of sleepiness during the day.
b. Symptoms include gradual or sudden attacks of sleepiness, occasional cataplexy (attack of muscle weakness while awake), sleep paralysis (inability to move while asleep), and hypnagogic hallucination (dreamlike experiences occurring at the onset of sleep).
c. Each of the symptoms of narcolepsy is interpreted as REM sleep intruding into wakefulness.
d. People with narcolepsy lack the hypothalamic cells that produce and release orexin.
e. Narcolepsy is currently treated with stimulant drugs such as methylphenidate (Ritalin).

Question 29

Periodic limb movement disorder:

Answer 29

Repeated involuntary movements of the legs and arms that can cause insomnia. The limb movements occur mostly during NREM sleep. Often treated with tranquilizers.

Question 30

REM behavior disorder:

Answer 30

Disorder where people move around vigorously during their REM periods apparently acting out their dreams. Likely due to the inability of the pons to inhibit spinal motor neurons.

Question 31

Night terrors:

Answer 31

An abrupt, anxious awakening from NREM sleep; this disorder is more common in children than adults.

Question 32

Sleepwalking:

Answer 32

Usually occurs during stages 3 or 4 early in the night; more common in children than adults; usually runs in families; more common when people are sleep deprived or under unusual stress.

Question 33

Sleep and Memory

Answer 33

a. Another function of sleep is improved memory. Young adults deprived of a night’s sleep show deficits on memory tasks. In contrast, if someone learns something and then goes to sleep, even for a short time, memory after sleeping is improved.
b. Research shows that the patterns that occur in the brain during sleep resembled those that occurred during learning, yet were more rapid during sleep. This suggests the brain replays its daily experiences during sleep and reinforces the learning through repetition.
c. Sleep strengthen memory selectively by reinforcing certain synaptic connections and weakening others to prevent over-activity of the brain.
d. During sleep, the brain also exhibits spindle activities of sleep spindles, which increase in number after new learning.

Question 34

Biological Perspectives on Dreaming

Answer 34

1. Activation-Synthesis Hypothesis: During sleep, many brain regions become activated, so the brain creates a story to make sense of all this activity.
2. Clinico-Anatomical Hypothesis: Either internal or external stimulation activates parts of the parietal, occipital, and temporal cortex. No visual information overrides the stimulation and no criticism of the prefrontal cortex censors it, so it develops into hallucinatory perceptions.

Question 35

Function of sleep:

Answer 35

• Energy conservation.
• Restoration of the brain and body.
• Memory consolidation